From bf8c7df203dc0d0cdaa59c72cc1424cbc746364b Mon Sep 17 00:00:00 2001
From: JJ Kasper <jj@jjsweb.site>
Date: Mon, 20 Apr 2020 14:57:47 -0500
Subject: [PATCH] Make sure to not show _error without 404 warning in some
 cases

---
 .../next/next-server/server/next-server.ts    |  3 ++-
 .../custom-error/test/index.test.js           | 25 ++++++++++++++++++-
 2 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/packages/next/next-server/server/next-server.ts b/packages/next/next-server/server/next-server.ts
index 878e5734f84c8..8c15bda295417 100644
--- a/packages/next/next-server/server/next-server.ts
+++ b/packages/next/next-server/server/next-server.ts
@@ -1321,7 +1321,8 @@ export default class Server {
     if (
       process.env.NODE_ENV !== 'production' &&
       !using404Page &&
-      (await this.hasPage('/_error'))
+      (await this.hasPage('/_error')) &&
+      !(await this.hasPage('/404'))
     ) {
       this.customErrorNo404Warn()
     }
diff --git a/test/integration/custom-error/test/index.test.js b/test/integration/custom-error/test/index.test.js
index b58df310cb4d9..c42259d0c148d 100644
--- a/test/integration/custom-error/test/index.test.js
+++ b/test/integration/custom-error/test/index.test.js
@@ -13,6 +13,7 @@ import {
 
 jasmine.DEFAULT_TIMEOUT_INTERVAL = 1000 * 60 * 2
 const appDir = join(__dirname, '..')
+const page404 = join(appDir, 'pages/404.js')
 const nextConfig = join(appDir, 'next.config.js')
 let appPort
 let app
@@ -27,6 +28,29 @@ const runTests = () => {
 const customErrNo404Match = /You have added a custom \/_error page without a custom \/404 page/
 
 describe('Custom _error', () => {
+  describe('dev mode', () => {
+    let stderr = ''
+
+    beforeAll(async () => {
+      appPort = await findPort()
+      app = await launchApp(appDir, appPort, {
+        onStderr(msg) {
+          stderr += msg || ''
+        },
+      })
+    })
+    afterAll(() => killApp())
+
+    it('should not warn with /_error and /404 when rendering error first', async () => {
+      stderr = ''
+      await fs.writeFile(page404, 'export default <h1>')
+      const html = await renderViaHTTP(appPort, '/404')
+      await fs.remove(page404)
+      expect(html).toContain('Module build failed')
+      expect(stderr).not.toMatch(customErrNo404Match)
+    })
+  })
+
   describe('dev mode', () => {
     let stderr = ''
 
@@ -42,7 +66,6 @@ describe('Custom _error', () => {
 
     it('should not warn with /_error and /404', async () => {
       stderr = ''
-      const page404 = join(appDir, 'pages/404.js')
       await fs.writeFile(page404, `export default () => 'not found...'`)
       const html = await renderViaHTTP(appPort, '/404')
       await fs.remove(page404)